In mobile communication systems, resources is frequency bands, the method for efficiently allocating limited frequency bands between users to use is a multiple access, and the connections method for distinguishing the connections of uplinks and downlinks in bi-directional communications is a multiplexing. A wireless multiple access and multiplexing scheme is platform technology which is the basis of wireless transmission technology for efficient usage of limited frequency bands, and is determined based on allocated frequency bands, the number of users, transmission rate, mobility, cell structures, radio environment, or the like. Orthogonal Frequency Division Multiplexing (OFDM), which is one of wireless transmission methods, is a kind of method of Multi Carrier Transmission/Modulation (MCM) methods using several carriers, and is to arrange pieces of input data in a row according to the number of carriers to be used, load data in respective carriers and transmit them. According to the multiple access scheme of a user, OFMD scheme is classified to OFDM-FDMA, OFDM-TDMA and OFDM-CDMA.
OFDM-FDMA (OFDMA) among them is suitable for fourth generation macro/micro cellular infra. According to the OFDMA, there is no interference within cells, the efficiency of frequency reuse is high and adaptive modulation is excellent. Furthermore, in order to make up for the weak points of OFDMA, it is possible to increases diversity and decrease the effect of interference between cells by using spread frequency hopping scheme, multiple antenna scheme, coding scheme, or the like. In particular, since OFDMA scheme is suitable in the case where a number of sub-carriers are used, it is effectively applied to wireless communication systems having a large area cell where the time delay spread is relatively big.
FIG. 1 is a diagram illustrating a method of transmitting and receiving data between a terminal (PSS: Personal Subscriber Station) and a Radio Access Station (RAS) using a conventional downlink power allocation method. As illustrated in FIG. 1, the Radio Access Station (RAS) is required to determine transmission power for each terminal for transmission and reception of data with terminals within service coverage. The radio access station transmits a data frame including a preamble or pilot to the terminal at step 101. Therefore, the terminal measures downlink quality information based on the preamble or pilot transmitted from the radio access station at step 102. The downlink quality information includes Signal-to-Interference and Noise Ratio (SINR). The terminal reports the downlink quality information to the radio access station through an uplink channel at step 103. In this case, the terminal reports downlink quality information for each channel to the radio access station with respect to entire frequency bands used by the radio access station at every frame.
The radio access station determines transmission power for each frequency band using the downlink quality information reported by the terminal at step 104. For example, as in FIG. 2, it may be possible to determine transmission power of a terminal 201 corresponding to a first band (FA1), transmission power of a terminal 202 corresponding to a second band (FA2) and transmission power of a terminal 203 corresponding to a third band (FA3) to be different from each other. Each band (FA1, FA2 or FA3) may be divided into several sub-channels. The radio access station performs scheduling according to the transmission power determined for each band and transmits a data frame to a corresponding terminal at step 105.
However, the downlink quality information is transmitted from a terminal to a radio access station through an uplink, so that the terminal must transmits the downlink quality information separately with uplink data which is to be actually transmitted through an uplink. Therefore, from a terminal standpoint, the downlink quality information for report of channel quality acts as additional data on the uplink, thereby resulting in loss of transmission quantity of data. Therefore, it is inefficient for the terminal to transmit downlink quality information for respective channels of entire bands at each frame.
Furthermore, in the prior art, transmission power is allocated in consideration of only one of transmission quantity and a service area rather than in consideration of both transmission quantity and a service area. Therefore, if transmission power for each terminal is allocated according to the conventional power allocation method, the service area is minimized when the transmission quantity of data of the radio access station is maximized, whereas the transmission quantity is minimized when the service coverage is maximized, so that a problem occurs in that the transmission quantity and service coverage can not be simultaneously improved.